This invention was made with Government support under Contract No. DE-FC21-95MC31176 awarded by the Department of Energy. The Government has certain rights in this invention.
In recent years, advanced gas turbines have trended toward increasing firing temperatures and efforts to improve cooling of the various turbine components. In a particular gas turbine design of the assignee, a high output turbine that uses a combination of steam and air cooling to meet a 60% combined cycle efficiency i s undergoing development. It will be appreciated that the design and construction of the turbine buckets and particularly the buckets of the fourth turbine stage of that turbine require optimized aerodynamic efficiency, as well as aerodynamic and mechanical bucket loading.
In accordance with an embodiment of the present invention, there is provided a unique turbine bucket airfoil profile for a turbine stage, preferably the fourth stage, which may be defined by a unique loci of points to achieve the necessary efficiency in loading requirements whereby improved turbine performance is obtained. It will be appreciated that the nominal profile given by the X, Y, Z coordinates of Table I, which follows, define this unique loci of points. The coordinates given in inches in Table I are for a cold, i.e., room-temperature profile for each cross-section of the bucket. Each defined cross-section is joined smoothly with adjacent cross-sections to form the complete airfoil shape. It will also be appreciated that as the bucket heats up in use, the profile will change as a result of stress and temperature. Thus, the cold or room-temperature profile is given by the X, Y, Z coordinates for manufacturing purposes. Because a manufactured bucket airfoil profile may be different than the nominal airfoil profile given in the following table, a distance of xc2x10.160 inches from the nominal profile in a direction normal to any surface location along the nominal profile and which includes any coating process, defines the profile envelope for this design. The design is robust to this variation without impairment of the mechanical and aerodynamic functions.
It will also be appreciated that the airfoil can be scaled-up or scaled-down geometrically for introduction into other similar turbine designs. Consequently, the X, Y and Z coordinates of the nominal airfoil profile given below are a function of the same constant or number. That is, the X, Y and Z coordinate values given in the Table may be multiplied or divided by the same constant or number to provide a scaled-up or scaled-down version of the bucket airfoil profile, while retaining the airfoil section shape.
In a preferred embodiment according to the present invention, there is provided a turbine bucket having a bucket airfoil shape in an envelope within xc2x10.160 inches in a direction normal to any airfoil surface location wherein the airfoil has an uncoated nominal profile substantially in accordance with Cartesian coordinates values of X, Y and Z set forth in inches in Table I wherein Z is a perpendicular distance from a plane normal to a radius of the turbine centerline and containing the X and Y values with the Z value commencing at zero in the X, Y plane at a radially innermost aerodynamic section of the airfoil and X and Y are coordinates defining the airfoil profile at each distance Z, the profiles at the Z distances being joined smoothly with one another to form the complete airfoil shape.
In a further preferred embodiment according to the present invention, there is provided a turbine bucket having an uncoated nominal airfoil profile substantially in accordance with Cartesian coordinates values of X, Y and Z set forth in inches in Table I wherein Z is a perpendicular distance from a plane normal to a radius of the turbine centerline and containing the X and Y values with the Z value commencing at zero in the X, Y plane at a radially innermost aerodynamic section of the airfoil and X and Y are coordinates defining the airfoil profile at each distance Z, the profiles at the Z distances being joined smoothly with one another to form the complete airfoil bucket profile, the X, Y and Z values being scaled as a function of the same constant or number to provide a scaled-up or scaled-down bucket airfoil.
In a further preferred embodiment according to the present invention, there is provided a turbine comprising a turbine wheel having a plurality of buckets, each of the buckets having an airfoil shape in an envelope within xc2x10.160 inches in a direction normal to any bucket airfoil surface location wherein the airfoil has an uncoated nominal profile substantially in accordance with Cartesian coordinates values of X, Y and Z set forth in inches in Table I wherein Z is a perpendicular distance from a plane normal to a radius of the turbine centerline and containing the X and Y values with the Z value commencing at zero in the X, Y plane at a radially innermost aerodynamic section of the airfoil and X and Y are coordinates defining the airfoil profile at each distance Z, the profiles at the Z distances being joined smoothly with one another to form the complete airfoil shape.
In a further preferred embodiment according to the present invention, there is provided a turbine comprising a turbine wheel having a plurality of buckets, each of the buckets having an uncoated nominal airfoil profile substantially in accordance with Cartesian coordinates values of X, Y and Z set forth in inches in Table I wherein Z is a perpendicular distance from a plane normal to a radius of the turbine centerline and containing the X and Y values with the Z value commencing at zero in an X, Y plane at the radially innermost aerodynamic section of the airfoil and X and Y are coordinates defining the airfoil profile at each distance Z, the profiles at the z distances being joined smoothly with one another to form the complete airfoil shape, the X and Y values being scaled as a function of the same constant or number to provide a scaled-up or scaled-down bucket airfoil.